This invention relates to a hybrid electric vehicle and more particularly, to a hybrid electric vehicle having a variable displacement engine which provides for improved fuel economy and load performance.
Various types of automotive vehicles have been designed and manufactured for the purpose of improving fuel economy. One type of vehicle, commonly known as a hybrid electric vehicle (xe2x80x9cHEVxe2x80x9d), utilizes both an internal combustion engine and one or more electric motors to generate power and torque. The electric motor(s) within a hybrid electric vehicle provides the vehicle with additional degrees of freedom in delivering the driver-demanded torque. Particularly, hybrid electric vehicles may have the flexibility of using the electric motor(s) as the sole source of torque at low load operating conditions. Additionally, at relatively high loads, a hybrid electric vehicle can employ or activate both the internal combustion engine and the electric motor(s) to supply the driver-demanded torque. Due to the ability of the electric motor(s) to augment the engine generated torque at high load operating conditions, hybrid electric vehicles typically employ relatively small or xe2x80x9cdownsizedxe2x80x9d internal combustion engines, which provide for improved fuel economy.
One drawback associated with these hybrid electric type vehicles is that the electric motors used within these vehicles receive power from an electrical energy storage device (e.g., a battery) which becomes depleted over time. When the electrical energy storage device or battery becomes depleted, the motors are no longer able to supplement the engine to deliver relatively high amounts of torque. This especially presents a problem in steady state high load situations (e.g., when towing or hauling heavy cargo), as the propulsion system (e.g., the engine and electric motor) may not be able to deliver the desired or demanded torque consistently and/or over an extended period of time. Thus, when high load steady state performance is required within a vehicle (e.g., within large trucks, sport-utility vehicles, and other vehicles that are often used for towing or hauling), the vehicle""s engine cannot be xe2x80x9cdownsizedxe2x80x9d and the hybridization-related fuel economy benefits cannot realized to the maximum potential.
Another type of vehicle, known as a variable displacement engine (xe2x80x9cVDExe2x80x9d) type vehicle, conserves fuel by selectively disabling or deactivating some of the engine""s cylinders under certain operating conditions. Particularly, during low engine load operation, a VDE type vehicle conserves fuel by operating on only some of the engine""s cylinders (e.g., on four, five, six, or seven of eight cylinders). During relatively high speeds and/or high load operation, a VDE type vehicle can meet the driver-demanded speed and/or torque by operating on all of the engine""s cylinders (e.g., on eight of eight cylinders). While these VDE type vehicles improve fuel economy and provide the torque required to satisfy relatively high load operation, they suffer from some drawbacks.
For example and without limitation, during relatively low and/or transient load operation (e.g., when the operating load varies significantly over a short period of time), the power train of a VDE type vehicle frequently shifts between various cylinder operating modes (e.g., the engine shifts between four, six, eight and ten cylinder operation). This frequent shifting between cylinder operating modes results in noise and vibration harshness (xe2x80x9cNVHxe2x80x9d) problems which are perceivable by the driver and which give the vehicle a xe2x80x9croughxe2x80x9d, xe2x80x9cinconsistentxe2x80x9d and/or xe2x80x9cnon-responsivexe2x80x9d feel or ride.
There is therefore a need for a vehicle which provides an improved fuel economy, which provides steady state high load performance, and which operates smoothly and responsively under transient load conditions.
It is a first object of the invention to provide an automotive vehicle which overcomes at least some of the previously delineated drawbacks of prior automotive vehicles.
It is a second object of the invention to provide an automotive vehicle which delivers and/or generates torque by use of a variable displacement engine and by use of one or more electric motors.
It is a third object of the invention to provide a hybrid electric vehicle having a variable displacement engine which allows the vehicle to perform under steady state high load operating conditions, while maintaining an improved fuel economy under relatively low or moderate load operating conditions.
It is a fourth object of the invention to provide an automotive vehicle having a variable displacement engine and which utilizes an electric motor to generate torque when operating under transient loads, thereby reducing the frequency of cylinder activation and deactivation within the variable displacement engine.
According to a first aspect of the present invention, a hybrid electric vehicle is provided. The hybrid electric vehicle includes a drive line; a battery which stores an amount of electrical charge and which selectively provides electrical power; and a sensor which is coupled to the battery and which is effective to estimate the amount of electrical charge and to generate a first signal based upon the estimated amount of electrical charge. The vehicle further includes an electric motor which is operatively coupled to the battery and to the drive line, which receives the electrical power from the battery, and which selectively provides torque to the drive line, and a variable displacement engine which is operatively coupled to the drive line and which selectively provides torque to the drive line. A controller is communicatively coupled to the variable displacement engine, to the electric motor, and to the sensor. The controller is effective to determine a requested torque to be provided to the drive line, to receive the first signal, and to partition the requested torque into an engine torque and a motor torque, based upon the first signal. The controller is further effective to cause the electric motor to provide the motor torque to the drive line, and to cause the variable displacement engine to provide the engine torque to said drive line.
According to a second aspect of the present invention, a method of delivering torque to a vehicle drive train is provided. The method includes the steps of providing a variable displacement internal combustion engine which selectively delivers torque to the drive train; providing a motor which selectively delivers torque to the drive train; providing an electrical charge storage device which supplies electrical energy to the motor; estimating an amount of charge which is held within the electrical charge storage device; receiving at least one signal from a driver-operated control; calculating a torque value based upon the at least one signal; partitioning the torque value into a desired motor torque and a desired engine torque based upon the estimated amount of charge and the torque value; causing the motor to deliver the desired motor torque to the drive train; and causing the variable displacement internal combustion engine to deliver the desired engine torque to the drive train, thereby powering the vehicle.